Cooling turbos down ?

[Monty Python]

ShaunTheSheep said:

The VAG EA888 2.0 TSi as fitted across the various A3, A4, A5, Golf GTI, Passat, Octavia Vrs etc. continues to pump oil through the IHI turbo after ignition off.

These engines use the VW507.00 oil which is AFAIK one of the strictest specifications regarding resistance to breakdown at high temperatures, but the oil is still pumped after ignition off suggesting 1050 degree C (max operating temp for the IhI turbo) is too hot for any oil technology just now.

Source: being too much of a geek, can't help it, http://files.engineering.com/download.aspx?folder=...

Reading that suggests that it's the cooling system that continues after the engine is switched off, not the oil system (p27, "After-Run Coolant Pump V51 protects the turbocharger bearings from overheating after engine shut-off.")

[philmots]

I'd suggest its bad to let the turbos get red hot and then turn off..

The turbos will go from red hot to a more normal temperature in seconds (if you've ever seen a pull on a rolling road you'd see) turning the engine off whilst they're glowing red would cook the oil left in the turbos - and also be quite hard to do as you'd probably be travelling quite quick.

If you've been hooning is suggest a brief 30 seconds to 1 minute of steady driving before switching off would be a good idea.

[RobGT81]

Monty Python said:

Reading that suggests that it's the cooling system that continues after the engine is switched off, not the oil system (p27, "After-Run Coolant Pump V51 protects the turbocharger bearings from overheating after engine shut-off.")

Yup, my Scirocco does this on a hot day. You can hear the pump running after you shut it off, for a couple of minutes sometimes.

[GroundEffect]

Monty Python said:

ShaunTheSheep said:

The VAG EA888 2.0 TSi as fitted across the various A3, A4, A5, Golf GTI, Passat, Octavia Vrs etc. continues to pump oil through the IHI turbo after ignition off.

These engines use the VW507.00 oil which is AFAIK one of the strictest specifications regarding resistance to breakdown at high temperatures, but the oil is still pumped after ignition off suggesting 1050 degree C (max operating temp for the IhI turbo) is too hot for any oil technology just now.

Source: being too much of a geek, can't help it, http://files.engineering.com/download.aspx?folder=...

Reading that suggests that it's the cooling system that continues after the engine is switched off, not the oil system (p27, "After-Run Coolant Pump V51 protects the turbocharger bearings from overheating after engine shut-off.")

Many OEMs use these now (I designed one recently). They're a pig.

[k-ink]

My girlfriends Nissan Figaro has a turbo timer. It is rather amusing on the slowest car on the roads

[MissChief]

I've never let my car idle after stopping outside my house but there are a couple of speed bumps and a 20 zone before my house so its around a minute of relatively slow travel before I get to the house so I've never bothered.

[Gwagon111]

MissChief said:

I've never let my car idle after stopping outside my house but there are a couple of speed bumps and a 20 zone before my house so its around a minute of relatively slow travel before I get to the house so I've never bothered.

That should suffice.

[si_xsi]

RobGT81 said:

Monty Python said:

Reading that suggests that it's the cooling system that continues after the engine is switched off, not the oil system (p27, "After-Run Coolant Pump V51 protects the turbocharger bearings from overheating after engine shut-off.")

Yup, my Scirocco does this on a hot day. You can hear the pump running after you shut it off, for a couple of minutes sometimes.

So is it the oil pump or cooling system making the noise? Mine makes a sort of continuous high pitch beep noise for maybe 10 secs max. Always wondered what it was.

[Tony427]

I had somewhat almost brand new breathed on Audi 100 Turbo some years back that had a large fan that blowed air from the cool side of the engine over the Turbo to cool it after switch off.

I could get home frrm a hard drive and go to bed in the bedroom facing the car to hear the fan still running full belt to cool the engine/ turbo.

One evening, after a year or so, the fan failed to cut off and next morning the battery was flat. So I removed the fuse feeding the fan. I ran the car for another 140k miles without any problems and at 169,000 miles the turbo and engine hadn't been touched and were perfect.

Theres a lot of rubbish talked about turbo timers and the like simply aimed to seperate you from your money.

hth,

cheers,

Tony

[james280779]

I only tend to do short journeys at the moment so I try to keep off the boost most of the time (difficult in an Esprit) then let it run for about a minute before turning it off.


Mine doesnt even have an intercooler ............. or fuel injection for that matter.

[Mr2Mike]

GroundEffect said:

Water cooling in turbo chargers is generally for cooling the housings, not the bearings. The oil cooling is still necessary for this function.

The water jacket is around the bearing housing, and thus cools the bearings and the oil within.

[Alex]

Water under pressure remains liquid beyond boiling point. To "turn to steam", you'd have to have a leak in your cooling system.

[y2blade]

J4CKO said:

I know conceived wisdom with turbos is to let them cool down before switching off, I remember reading that this was to allow the oil to circulate whilst the turbo, sometimes glowing red can cool down a bit so when the oil stops being pumped around it doesnt carbonise in the bearings.

Is this still as critical ? given that a lot of turbos are now water cooled and most use synthetic oil, does this still carbonise ? do diesel turbos get as hot as petrol ones, my thinking is that you wouldnt want to stick your tongue on it but they dont get quite as hot as diesels tend to run a bit cooler (or do they ?) , but the heat may be more a function of masses of compressed air and than combustion.

I suppose it is good practice to err on the side of caution, but is this advice still valid ? does anyone still use a Turbo Timer outisde of massively boosted jap imports ?

I always let it cool down by idling for 2mins minimum prior to shutting off....if I've been driving hard I open the bonnet while on cool down too.

It is a good habit I got into with my First Volvo T5, and have done the same with every turbo (petrol and diesel) I have owned or driven since.

[Olivera]

Most of the advice here is relevant if you are driving a 1982 turbo car, but my 10 year old CupraR, and as others have mentioned a 20 year old Porsche 944, all have secondary water pumps that feed coolant to the turbo after the vehicle is switched off. This is sufficient for almost all road driving scenarios, however I concede letting it cool down over an extended period is prudent after track driving.

[j4ckos mate]

I always drive or A4 tdi off boost within half a mile of home, then leave it running for a few seconds whilst all the kids crap is taken out of the boot, and the kids open the gates

[ShaunTheSheep]

j4ckos mate said:

and the kids open the gates

You've just done more to convince me that kids are a good idea than my better half has in 7 years!

[GroundEffect]

Alex said:

Water under pressure remains liquid beyond boiling point. To "turn to steam", you'd have to have a leak in your cooling system.

It's a linear relationship between temperature of phase change and pressure. Trust me, you can boil water at any pressure as long as the temperature is correct.

[dancarro]

My WRX has just clocked past 155K, and I have never done this. It's completely stock, but does get some spirited driving now and then.

Unless your ragging it around a track then into the pits, i can't see the need.

I'm sure somebody else will have a different point of view, and experience on this though.

[digger the goat]

GroundEffect said:

It's a linear relationship between temperature of phase change and pressure. Trust me, you can boil water at any temperature as long as the pressure is correct.

Fixed that for you !!

Edited by digger the goat on Tuesday 7th May 15:44

Edited by digger the goat on Tuesday 7th May 15:46

[Alex]

GroundEffect said:

It's a linear relationship between temperature of phase change and pressure. Trust me, you can boil water at any pressure as long as the temperature is correct.

I agree, but in the context of car cooling systems, you will not get "steam" in the system without a pressure leak.